Hot-swap protection circuit

ABSTRACT

Embodiments of the present invention provide methods and circuitry for protecting a circuit during hot-swap events. Hot swap protection circuitry includes as overcurrent detection circuit which decouples power from a load. Circuitry is provided to detect ground-fault conditions. Noise detection circuitry is provided to reduce noise in the power that is delivered to the load.

CROSS-REFERENCES TO RELATED APPLICATIONS

[0001] The present application is related to and claims priority fromU.S. Provisional Application No. 60/258,004, filed Dec. 22, 2000.

STATEMENT AS TO RIGHTS TO INVENTIONS MADE UNDER FEDERALLY SPONSOREDRESEARCH OR DEVELOPMENT

[0002] NOT APPLICABLE

REFERENCE TO A “SEQUENCE LISTING,” A TABLE, OR A COMPUTER PROGRAMLISTING APPENDIX SUBMITTED ON A COMPACT DISK.

[0003] NOT APPLICABLE

BACKGROUND OF THE INVENTION

[0004] The present invention relates generally to integrated circuits.More particularly, the invention relates to a method and circuitry forhot-swap protection circuits.

[0005] A hot swap operation is an insertion action or a removal actionof a device while the system using it is receiving power, coupling thepower from the system to the device. Such an operation can causeexternal capacitors to draw currents high enough to disturb systemoperations or even cause permanent damage to either or both the deviceand the system.

[0006] Hot-swap protection circuits enable electronic circuits to beconnected to each other and disconnected from each other while powered.Hot-swap protection circuits are required in many applications where itis not practical to shut down an electronic system while replacing oradding circuit boards to it. Such protection circuits, or systems, areused in telephone switching hubs, corporate network server hubs, and inlaptop or desktop computers with PCMCIA connectors. All of the examplesrequire connection or disconnection under power and so on.

[0007] Conventional hot-swap protection circuits employ connectors withat least one set of sensor pins, which are a set of extra long and extrashort pins, connected to voltage detectors. These sensor pins allowimmediate detection of connection and/or disconnection by sensing thepresence and/or absence of the applied voltage. It is well known that asingle set of sensor pins-whether at the top, middle, or bottom-mightnot be enough to detect a hot-swap event.

[0008] For the best reliability, it is often necessary to use two setsof sensor pins, one set at the top and one set at the bottom of ahot-swappable card. Adding additional sets of sensor pins increasereliability, but increases costs to the overall system. Additionally,conventional hot-swap protection systems using sensor pins do not alwaysdetect the application or removal of power to a system.

BRIEF SUMMARY OF THE INVENTION

[0009] The present invention provides a method and circuitry for hotswap operations. Application of power from a source of power is detectedby first circuitry. A switch couples the power to the device in agradual manner in responsive to the first circuitry. Circuitry isprovided which detects an overcurrent condition in which the currentdraw by the device exceeds a predetermined level. The switch decouplesthe device from the power responsive to the circuitry. Circuitry isprovided detects events in which power is removed momentarily, as occursin a ground-fault condition, or permanently as in a disconnect event,and in response thereto a signal is produced indicative of theoccurrence. Circuitry, which is responsive to noise in the power, isoperatively coupled with the switch which varies its conductance inresponse to the detected noise.

[0010] Embodiments of the present invention achieve their purposes andbenefits in the context of known circuit and process technology andknown techniques in the electronic and process arts. Furtherunderstanding, however, of the nature, features, and advantages of thepresent invention is realized by reference to the latter portions of thespecification, accompanying drawings, and appended claims. Otherfeatures and advantages of the present invention will become apparentupon consideration of the following detailed description, accompanyingdrawings, and appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

[0011]FIG. 1 is a simplified high-level block diagram of an electronichot-swap protection circuit, according to one embodiment of the presentinvention;

[0012]FIG. 2 is a simplified high-level schematic diagram of thehot-swap protection circuit of FIG. 1, according to one embodiment ofthe present invention;

[0013]FIG. 3 is a simplified high-level schematic diagram of thehot-swap protection circuit of FIG. 1, according to another embodimentof the present invention;

[0014]FIG. 4 is a simplified high-level block diagram of an electronichot-swap protection circuit, according to another embodiment of thepresent invention;

[0015]FIG. 5 is a simplified high-level schematic diagram of thehot-swap protection circuit of FIG. 4, according to one embodiment ofthe present invention;

[0016]FIG. 6 is a simplified high-level schematic diagram of thehot-swap protection circuit of FIG. 5, according to another embodimentof the present invention;

[0017]FIG. 7 is a simplified high-level schematic diagram of thehot-swap protection circuit of FIG. 4, according to another embodimentof the present invention; and

[0018]FIG. 8 is a simplified high-level schematic diagram of thehot-swap protection circuit of FIG. 7, according to one embodiment ofthe present invention.

DETAILED DESCRIPTION OF THE INVENTION

[0019]FIG. 1 is a simplified high-level block diagram of an electronichot-swap protection circuit 100, according to one embodiment of thepresent invention. FIG. 1 shows a detector 102 coupled in series, via aconnector 105, to an electrical power source 107. Detector 102 alsocouples in series to a fast-disconnect, slow-reconnect switch 110.Switch 110 couples in series along a power supply conductor between aload 112 (circuit to be protected, target circuit, device, etc.) andpower source 107. Detector 102 includes an overcurrent detector module115 and a control circuit 117. Detector module 115 is series-coupledbetween switch 110 and a first terminal of connector 105. Controlcircuit 117 is coupled to a second terminal of connector 105. Detectormodule 115 includes an output that feeds into control circuit 117.

[0020] In this specific embodiment, detector module 115 and switch 110couple to the positive terminal of power supply 107, and control circuit117 couples to the negative terminal of power supply 107. Alternatively,detector module 115 and switch 110 can be located on the negativeterminal of power source 107, with appropriate modifications to thecircuitry.

[0021] In operation, detector 102 detects whether load 112 ishot-swapped in, i.e., reconnected to power source 107. When detector 102detects a reconnect event, it outputs a hot-swap occurrence indication,or “indication,” or “control signal.” More specifically, detector 102sends a hot-swap occurrence indication, i.e., a reconnect controlsignal, to switch 110 instructing it to close, i.e., turn on, inaccordance with the invention.

[0022] Hot-Swap Occurrence Indication

[0023] In this and in other embodiments of the present invention, thehot-swap occurrence indication can serve other functions and will dependon the specific application. For example, the indication can be coupledto drive an LED to notify a user of the hot-swap occurrence. Theindication can also be coupled to a controller or microprocessor in theform of an interrupt signal, for example, so that appropriate processingcan be performed.

[0024] In this specific embodiment, the reconnect control signal isproduced by control circuit 117. Also, in this specific embodiment,switch 110 opens quickly but closes slowly. Upon reconnection, theconductivity of switch 110 gradually increases to a fully conductivestate, i.e., non-binary change of state that is gradual as opposed todiscrete.

[0025] Upon detection of a reconnect event, detector module 115 producesa signal indicative of a reconnect event. The signal feeds to controlcircuit 117 which then produces an indication signal and a controlsignal. The control signal feeds to switch 110. As will be explainedbelow, the control signal is of a nature as to cause switch 110 togradually increase its conductance (i.e., gradually decrease itsresistance).

[0026] A reconnect event is typified by a detection of a presence ofvoltage following the absence of current. The term “reconnect” impliesthe load 112 was previously connected. However, it is possible that aload might never have been connected to the powered system, in whichcase the term “connect” is more appropriate. For purposes of thisdisclosure, however, the terms “reconnect” and “connect” are usedinterchangeably, since both situations are the same from the point ofview of a hot swap operation.

[0027]FIG. 2 is a simplified high-level schematic diagram of a hot-swapprotection circuit 100 in accordance with an illustrative embodiment ofthe present invention. Hot-swap protection circuit 100 is implementedwith commonly available integrated circuits including discrete-activeand -passive components (see FIGS. 6 and 8, for example). Hot-swapprotection circuit 100 includes detector 102 and switch 110, both ofwhich are located on the negative terminal of power source 107.Alternatively, in other embodiments, detector 102 and switch 110 can belocated on the positive terminal of power source 107 (as in FIG. 1),with appropriate modifications to the circuitry.

[0028] In this specific embodiment, load 112 couples in parallel to acapacitor 120. FIG. 2 shows a schematic of the switch. Typically, theswitch 110 is a MOSFET device such as the one shown in FIG. 2 having apart number BUK456. Of course, other commercially available switches canbe substituted; e.g., FIG. 6 shows a FET having a part number IRF2807.

[0029] Detector module 115 includes an operational amplifier 127, orop-amp 127, configured to output a hot-swap occurrence indication, e.g.,a reconnect control signal. The non-inverting input of op-amp 127couples to switch 110 and inverting input of op-amp 127 couples to thenegative terminal of power source 107 via a voltage source 130. Aresistor 132 couples between the inverting and non-inverting inputs ofop-amp 127. In this specific embodiment, for example, op-amp 127 isimplemented with an integrated circuit operational amplifier identifiedby the part number MC33174. Other commercially available op-amps orsimilar devices can be used.

[0030] Control circuit 117 includes a diode 135, resistor 137, and aZenor diode 140 coupled in series between the positive and negativeterminals of power source 107. A resistor 142 and a capacitor 144 couplein parallel between the positive and negative terminals of power source107. A resistor 147 and a capacitor 150 couple in series with capacitor144. A transistor 152 couples between a gate switch 110 (node V_(GATE))and the negative terminal of power source 107. Transistor 152 has a gatecoupled to the output of op-amp 217. Node V_(GATE) couples controlcircuit 117 to switch 110.

[0031] In operation, generally, hot-swap protection circuit 100 of FIG.2 functions to enable the soft (gradual) application of the voltage atnode V_(IN) to the load 112. This soft application reduces the stress tothe components within load 112 as well as to capacitor 120. Such stresscan cause physical damage to these components. For example, if aninstantaneous voltage is applied across load 112 or capacitor 120, it istheoretically possible to cause infinite current flow through load 112or capacitor 120. This can either degrade them or immediately cause themto explode, causing physical damage and possible destruction.

[0032] Suppose that after load 112 is reconnected for a sufficientamount of time such that the voltage at node V_(OUT) settles to avoltage close that at node V_(IN), and a steady state current flowthrough load 112 is established. The difference between voltages atnodes V_(OUT) and V_(IN) is simply the load current through load 112times the sum of the resistances of resistor 132 and a resistance Rdsonof switch 110 in the conducting state.

[0033] Operation of Detector 102 upon Reconnection

[0034] Upon reconnection, hot-swap protection circuit 100 enables a softturn-on of switch 110 through resistor 147. The soft start sequence isas follows. First, assume that all of the capacitors in control circuit117, as well as capacitor 120 across the load 112, are discharged sothat the potential at node V_(IN) at connector 105 is at zero potential.Second, power source 107 couples to detector module 102 via connector105. The application of the voltage at node V_(IN) at the output of theconnector 105 causes the presence of a voltage E_(IN), i.e., voltage ofpower source 107 at node N. Capacitor 144 then charges through resistor137 to 12V, the voltage of which is determined and limited by Zenordiode 140. In other embodiments, Zenor diode 140 can have other values.During this time, the voltage at node V_(GATE) ramps up from zeropotential through resistor 147, implementing a “soft” or slow turn-on ofswitch 110. The voltage at node V_(OUT) then quickly ramps up from azero potential to the voltage at node V_(IN). The ramp-up rate isdetermined by the turn-on rate of switch 110 and the size of capacitor120 across the load 112.

[0035]FIG. 3 is a simplified high-level schematic diagram of a hot-swapprotection circuit 100 in accordance with another illustrativeembodiment of the invention. Hot-swap protection circuit 100 of FIG. 3is similar to that of FIG. 2. In the embodiment shown in FIG. 3,detector 102 includes circuit 160.

[0036] Circuit 160

[0037] Circuit 160 includes an operational amplifier 162, or op-amp 162.An output of op-amp 162 couples to the gate of switch 110, or nodeV_(GATE), via a resistor 165. Node V_(GATE) couples between resistor 147and capacitor 150 via a diode 167. A bias voltage source 170 couples inparallel to capacitor 150. In this particular embodiment, bias voltagesource 170 is a voltage divider. Bias voltage source 170 includes aresistor 172 and a resistor 175. An inverting input of op-amp 162couples between resistors 172 and 175 via a resistor 177 and to nodeV_(GROUND) via a capacitor 180.

[0038] In the specific illustrative embodiments of FIGS. 2, 3, 5, 6, 7,and 8, V_(GROUND) located at the positive terminal of power source 107because the protection circuit of these specific embodiments operates inthe negative voltage range. The specific voltage range in which theprotection circuit operates will depend on the specific application. Forexample, the operating voltage range can also be in both the negativeand positive voltage ranges. In some embodiments, the operating voltagerange can only positive voltage ranges, for example, whereV_(GROUND)=0V.

[0039] Operation of Circuit 160

[0040] Circuit 160 protects load 112 from noise that might be present inpower source 107. Circuit 160 operates in conjunction with switch 110 toeffectively function as a low pass filter of the power from power source107, thus reducing the effects of noise present in the power. The op-amp162 is configured as a voltage follower. Noise from power source 107will propagate through network 170 to the inverted input 13 of op-amp162 through the network of resistor 177 and capacitor 180. The noisecomponents will cause a differential input to appear at the input ofop-amp 162. The resulting output of op-amp 162 will drive switch 110 toalter its conductivity as a function of the noise. This in turn altersthe current flow to load 112. Consequently, the power delivered to load112 will be effectively low-pass filtered by the switch. Thus, byaltering the conductivity of the switch 110 in response to noise presentin the power, the noise components in the power delivered to the load112 can be reduced.

[0041] Operation of Overcurrent Detector Module 115 (Load Connected)

[0042] The following description assumes that load 112 has beenconnected to power source 107 through switch 110, which is on, andthrough overcurrent detector module 115. As long as the voltage dropacross resistor 132 is less than voltage source 130, e.g., Vcl=100 mV,the output of op-amp 127 will be low, or at the voltage at node V_(IN).This keeps transistor 152 of control circuit 117 off and node V_(GATE)high which keeps switch 110 on.

[0043] An overcurrent condition is one where load 112 demands a muchhigher than normally expected current. For example, suppose that thecurrent is so high that the voltage drop across resistor 132 is greaterthan 100 mV. This causes the non-inverting input of op-amp 127 to becomemore positive than its inverting input. Note that the voltagedifferential across the non-inverting and the inverting inputs occurswhen a detected overcurrent condition is detected. In this specificexample, an overcurrent is detected when the voltage drop acrossresistor 132 is greater than 100 mV, or if greater than 10 amps ofcurrent flow through resistor 132. The threshold current which definesan overcurrent condition can be predetermined by setting voltage levelof voltage source 130 accordingly.

[0044] Upon detection of an overcurrent condition, overcurrent detectormodule 115 causes the output of op-amp 127 to go high, or +12V. Thisturns on transistor 152 to discharge capacitor 150 to the voltage atnode V_(IN). This discharged of capacitor 150, Vcl=˜0V, causes switch110 in switch 110 to turn off which results the disconnection of load112. After switch 110 turns off, the output of op-amp 127 drops backdown to 0V, or the voltage at node V_(IN), because the current throughresistor 132 is cut off. Also, capacitor 150 begins to recharge.

[0045] The same logical high signal with respect to node V_(IN) (whichis available from op-amp 127) becomes an indication output. Thisindication output indicates an overcurrent fault shut down.

[0046]FIG. 4 is a simplified high-level block diagram of an electronichot-swap protection circuit 100, according to another embodiment of thepresent invention. Hot-swap protection circuit 100 FIG. 4 is configuredsimilarly to that of FIG. 1 except that circuit 100 of FIG. 4 includes adetector 181 that detects whether load 112 is hot-swapped out, i.e.,disconnected from power source 107. In this specific embodiment,detector 102 couples in parallel to a switch 110. Switch 110 couples inseries to a terminal of power source 107 via connector 105 and to load112.

[0047] When detector 102 detects a disconnect event, it outputs ahot-swap occurrence indication, or “indication,” or “control signal.”More specifically, detector 102 sends a hot-swap occurrence indication,i.e., a disconnect control signal, to switch 110 causing it to open,i.e., turn off. Switch 110 opens quickly.

[0048] Hot-Swap Occurrence Indication

[0049] As stated above, the hot-swap occurrence indication can serveother functions which depend on the specific application. For example,the indication can be coupled to drive an LED to notify a user of thehot-swap occurrence. The indication can also send a signal to acontroller or microprocessor as an interrupt signal to performappropriate processing in the occurrence of a disconnect. During adisconnect event in a storage device, for example, certain cleanupoperations can be performed before the drive loses all of its power.

[0050]FIG. 5 is a simplified high-level schematic diagram of a hot-swapprotection circuit 100, which in some embodiments of the presentinvention, can be used to implement the hot-swap protection circuit ofFIG. 4. Like hot-swap protection circuit 100 of FIG. 4, that of FIG. 5is implemented with commonly available integrated circuits includingdiscrete-active and-passive components.

[0051] Hot-swap protection circuit 100 of FIG. 5 includes detector 181and switch 110, both of which are located on the negative terminal ofpower source 107. Alternatively, in other embodiments, detector 181 andswitch 110 can be located on the positive polarity conductor of thepower source 107 (as in FIG. 4), with appropriate modifications to thecircuitry.

[0052] In this specific embodiment, detector 181 of FIG. 5 includes thesame elements and configuration as that of FIG. 2 with a few exceptions.Detector 181 of FIG. 5 includes a ground-fault protection circuit 185 inplace of overcurrent protection circuit 115 of FIG. 2.

[0053] Upon detection of a disconnect event, detector module 185 sendsan output indication, or “signal,” to control circuit 117. Accordingly,if the signal is triggered by a disconnect event, control circuit 117sends a disconnect control signal to switch 110 instructing it to open.

[0054] Switch 110 couples between the non-inverting input and theinverting input of an op-amp 187 via a voltage source 192.

[0055] Operation of Detector 181 upon Disconnection

[0056] In operation, hot-swap protection circuit 100 of FIG. 5,functions as a load-disconnect protection circuit. Prior todisconnection, assuming that load 112 is powered normally andoperational. The voltage at node V_(OUT) is approximately equal to thatat node V_(IN), less the voltage drop across switch 110. The voltagedrop across switch 110 is such that the voltage at node V_(OUT) is morepositive than that at node V_(IN), because current is being supplied toload 112 through switch 110 from node V_(IN). Op-amp 187 of detector 181connects across switch 110. The non-inverting input of op-amp 187couples to a voltage source Vos 192. The value of voltage source 192 isapproximately −10 mV and can vary depending on the specific application.The −10 mV ensures that the output of op-amp 187 is low relative to thevoltage at node V_(IN), regardless of the current flow of load 112, orregardless of any finite built-in offset voltages of op-amp 187(assuming that the input offset voltage of op-amp 187<10 mV). This keepstransistor 152 off so that node V_(GATE) is charged to 12V, keepingswitch 112 on.

[0057] Operation of Ground-Fault Protection Circuit 185 (Load GetsDisconnected)

[0058] The following description assumes that at some time T1 connector105 disconnects due to a ground fault-condition. Because there are nocapacitors connected between nodes V_(GROUND) and V_(IN), the voltage atnode V_(IN) has the tendency to move towards the voltage at nodeV_(GROUND). However, this does not happen because the charge oncapacitor 120, which was initially charged to the voltage at nodeV_(OUT). Capacitor 120 sustains a current flow from node V_(OUT) to nodeV_(IN). As long as there is available charge in capacitor 120 to sustainthe current needed by detector 181, it will function properly.

[0059] In operation, detector 181 recognizes immediately that thevoltage across switch 110 is now reversed, i.e., the voltage at nodeV_(OUT) is more positive than that at node V_(IN). The output of op-amp187 goes high to turn on transistor 152, which in turn dischargescapacitor 150. This causes switch 110 in switch 110 to turn off whichresults the disconnection of load 112. This also stops the discharge ofcapacitor 120 by the detector 181.

[0060] In some embodiments of the invention, because the logical highsignal that op-amp 187 outputs also functions as a hot-swap occurrenceindication, the indication can be sent to other circuits, e.g., LED,controller, microprocessor, etc., for other purposes.

[0061] This circuit technique detects the presence (indication low) orabsence (indication high) from detector 181, and represents an automaticground fault detection without the need for separate ground sense pinsas needed in the prior art.

[0062] It is to be understood that this specific implementation asdepicted and described herein is for illustrative purposes only andshould not limit the scope of the claims herein, and that alternativecircuit implementations exist for the same functionality. For example,any IC chip, proprietary or otherwise, can be used to implements thecircuits described herein.

[0063] The foregoing circuits can be readily implemented using any of anumber of commercially available integrated circuit devices. Forexample, FIG. 6 illustrates how the hot-swap protection circuitaccording to the present invention as shown in FIG. 5 can be providedusing conventional hot-swap IC devices. Attached as Appendix A is a datasheet for the IC device. Following is a description of the pin outs ofthe chip:

[0064] Pin 1 (INV) provides an invert input function. The invert inputcontrols GSNSin's polarity. When invert input is high compared to AGND,then GSNSin low indicates an insertion/removal event. When invert inputis low, then GSNSin high indicates an insertion/removal event.

[0065] Pin 15 (GSNSin) provides a ground sense input. The INV pincontrols the polarity sense of this input. A 3uA internal pull-upcurrent source causes logic high when there is no connection at thispin. With INV low or connected to AGND, a GSNSin low (or connected toAGND) will keep RSTout and GATE low, and the external power switch, Q1,off. A disconnected GSNSin pin or when Vcc is applied to it will allownormal operation.

[0066] Pin 2 (VCCin) is the supply voltage positive power-supply voltageinput.

[0067] Pin 3 (SHNToff) is the shunt off pin. This pin serves to controlthe enabling of the shunt circuit. When the pin is high compared toAGND, then the shunt regulator is in off position. A low level at thispin activates the shunt regulator.

[0068] Pin 4 (CAPin) is an active lowpass filter capacitor input. Theoutput of the power active filter tracks this pin. Adding an external RCnetwork matching the input noise with respect to the 3db point of thefilter could reduce the noise to a minimum.

[0069] Pin 5 (VDROP) is an active filter offset voltage pin. This pinsets the drop out MOSFET voltage across the active filter.

[0070] Pin 6 (SLOPE) is a slope input pin. This input controls thecurrent slope during power up and controls inrush currents. Addingexternal capacitors to this pin allow regulation and adjustment of therate of the current slope.

[0071] Pin 7 (OFFTM) is the off-time pin. The OFFTM pin sets the delaytime between powerdown and restart of IXHQ100. Delay time can beincreased by adding external capacitors to this pin.

[0072] Pin 8 (AGND) is the ground pin. This pin provides a system zeroreference pin.

[0073] Pin 9 (VDDout) is the regulator output voltage pin. The regulatoroutput voltage provides current to drive the external circuits withrespect to AGND.

[0074] Pin 10 (VCL) is the vercurrent threshold bias voltage pin. Thispin sets the overcurrent threshold bias voltage.

[0075] Pin 11 (SOURCE) is the current input sensor pin. This serves asthe input pin for sensing current through the power device with respectto AGND.

[0076] Pin 12 (GATE) in the output pin. This is control voltage pin fordriving an external MOSFET.

[0077] Pin 13 (OUTsns) is the out sensor signal pin. This signal pinsenses the output voltage of the circuit.

[0078] Pin 14 (RSTout) is the output reset pin. A low at this pinindicates detection of an insert/removal event or overcurrent detection.

[0079] Pin 16 (NC) N/A Not Connected

[0080]FIG. 7 is a simplified high-level schematic diagram of a hot-swapprotection circuit 100, which in some embodiments of the presentinvention, can be used to implement the hot-swap protection circuit ofFIG. 4. Hot-swap protection circuit 100 of FIG. 7 is similar to that ofFIG. 5 except that it includes a filter 160. In this particularembodiment, filter 160 is an active filter. Also, filter 160 of thisspecific embodiment is implemented with commonly available integratedcircuits and discrete active and passive components.

[0081] Filter 160 of FIG. 7 includes the same elements and is configuredsimilarly to that of FIG. 3 except that the non-inverting input ofop-amp 162 couples to the drain of switch 110 as well as to theinverting input of op-amp 187.

[0082]FIG. 8 further illustrates how the hot-swap protection circuitaccording to the present invention as shown in FIG. 5 can be providedusing conventional hot-swap IC devices. The circuit shown in FIG. 8 usesthe IC device described in the data sheet of Appendix A that can be usedto implement the hot-swap protection circuit of FIG. 7. In addition,FIG. 1 in the data sheet of Appendix A shows a configuration whichimplements a hot swap protection circuit according to the presentinvention as shown in FIG. 3.

[0083] Other similar commercially available IC devices can be used toimplement the hot swap protection circuits disclosed herein. Forexample, Linear Technology sells a line of hot swap controllers such aspart nos. LT1640AH and LT1640AL. Texas Instruments Incorporated sells aline of hot swap IC devices such as TPS2320 and TPS2321. MaximIntegrated Products sells IC devices such as the MAX5904 which can beused. The disclosed hot swap protection circuitry according to thepresent invention can be made using such IC devices in conjunction withappropriate external components.

[0084] Specific embodiments of the present invention are presented abovefor purposes of illustration and description. The full description willenable others skilled in the art to best utilize and practice theinvention in various embodiments and with various modifications suitedto particular uses. After reading and understanding the presentdisclosure, many modifications, variations, alternatives, andequivalents will be apparent to a person skilled in the art. Theforegoing, therefore, is not intended to be exhaustive or to limit theinvention to the specific embodiments described. The claimed inventionis intended to be accorded the widest scope consistent with theprinciples and novel features disclosed herein, and as recited in thefollowing claims.

What is claimed is:
 1. A method for protecting a target circuit, the method comprising: detecting power from a source of power; coupling the power to the target circuit in a gradual manner; detecting noise components in the power; and varying the amount of power delivered to the target circuit in response to the noise component.
 2. The method of claim 1 wherein the step of coupling includes controlling the conductivity of a transistor device, the transistor device having series-connection between the source of power and the target circuit.
 3. The method of claim 1 wherein the step of coupling includes controlling the conductivity of a transistor device, the transistor device having series-connection between the source of power and the target circuit.
 4. A method for protecting a target circuit, the method comprising: detecting power from a source of power; coupling the power to the target circuit in a gradual manner; detecting when a current supplied to the target circuit exceeds a threshold; and decoupling the power in response to detecting that the current supplied to the target circuit exceeds a threshold.
 5. A circuit comprising: a switch configured to couple a target circuit with a source of power; a first detector configured to detect power provided by the source of power, the first detector operatively coupled with the switch, wherein the switch closes responsive to the first detector; and a second detector configured to detect noise in the power, the second detector operatively coupled to the switch, wherein a conductivity of the switch varies responsive to the second detector.
 6. The circuit of claim 5 wherein the second detector couples between the source of power source and a gate of the switch.
 7. The circuit of claim 5 further including a positive terminal and a negative terminal, wherein the switch is a transistor device having a gate, a source, and a drain, wherein the second detector comprises: a bias voltage source; an operational amplifier having: an inverting input coupled with the positive terminal and coupled with the bias voltage source; a non-inverting input coupled with a negative terminal; and an output coupled to the gate of the switch.
 8. The circuit of claim 7 wherein the output of the operational amplifier couples with the first detector.
 9. The circuit of claim 7 wherein the bias voltage source coupled with the first detector.
 10. The circuit of claim 9 wherein the bias voltage source is a voltage divider.
 11. A circuit comprising: a switch configured to couple a target circuit with a source of power; a first detector configured to detect power from a source of power, the first detector operatively coupled with the switch, wherein the switch closes responsive to the first detector; and a second detector configured to detect when a current supplied to the target circuit exceeds a threshold, wherein the switch opens responsive to the second detector.
 12. The circuit of claim 11 wherein the switch closes at a slower rate than it opens.
 13. The circuit of claim 11 wherein the switch is characterized by having a variable conductance, wherein the switch closes at a slow rate such that its conductance is gradually increased.
 14. The circuit of claim 11 wherein the first detector and the switch are coupled to the positive terminal of the source of power.
 15. The circuit of claim 11 wherein the first detector and the switch are coupled to the negative terminal of the source of power.
 16. The circuit of claim 11 wherein the switch comprises a first transistor coupled between the source of power and the target circuit, the first transistor having a control node coupled to the first detector.
 17. The circuit of claim 16 wherein the first transistor is a FET transistor.
 18. The circuit of claim 16 further comprising a filter, wherein the control node of the first transistor couples to the first detector via the filter.
 19. The circuit of claim 11 wherein the second detector comprises a first op-amp operatively coupled between the first detector and the switch.
 20. The circuit of claim 19 wherein the second detector further comprises a resistor coupled between the first op-amps inputs.
 21. The circuit of claim 19 wherein the second detector further comprises a second power source coupled between one of the first op-amp inputs and the source of power.
 22. The circuit of claim 11 wherein the first detector comprises: a second transistor; and a capacitor coupled between the conduction nodes of the second transistor
 23. A circuit comprising: a switch configured to couple a target circuit with a source of power; a first detector configured to detect power from the source of power, the first detector operatively coupled with the switch, wherein the switch closes responsive to the first detector; and a second detector configured to detect when the source of power is decoupled from the target circuit, wherein the switch opens responsive to the second detector.
 24. The circuit of claim 23 wherein the switch comprises a first transistor coupled between the source of power and the target circuit, the first transistor having a control node coupled to the first detector.
 25. The circuit of claim 23 further comprising a filter, wherein the control node of the first transistor couples to the first detector via the filter.
 26. The circuit of claim 23 wherein the second detector comprises a first op-amp operatively coupled between the first detector and the switch.
 27. A circuit comprising: a switch configured to couple a target circuit with a source of power; a first detector configured to detect power from the source of power, the first detector operatively coupled with the switch, wherein the switch closes responsive to the first detector; and a second detector configured to detect a voltage change from a non-zero voltage towards a zero voltage, wherein the switch opens responsive to the second detector.
 28. The circuit of claim 27 wherein the switch comprises a first transistor coupled between the source of power and the target circuit, the first transistor having a control node coupled to the first detector.
 29. The circuit of claim 28 further comprising a filter, wherein the control node of the first transistor couples to the first detector via the filter.
 30. The circuit of claim 27 wherein the second detector comprises a first op-amp operatively coupled between the first detector and the switch.
 31. A circuit for coupling a power source to a device comprising: first circuit means for detecting a connection event wherein a connection is made between the first circuit and the power source; second circuit means, responsive to the first circuit means, for varying the amount of power from the power source that is applied to the device; third circuit means for filtering electrical noise originating from the power source to produce a filtered signal; and fourth circuit means for producing a control signal responsive to the filtered signal, the second circuit means further being responsive to the control signal so that the amount of power that is applied to the device varies in response to the electrical noise.
 32. A circuit for coupling a power source to an electronic device comprising: first circuit means for detecting a connection event wherein a connection is made between the first circuit and the power source; second circuit means, responsive to the first circuit means, for coupling power from the power source to the electronic device so that power is applied to the electronic device in a gradual manner; third circuit means for detecting an overcurrent event wherein the electronic device draws current from the power source exceeding a predetermined level of current; and fourth circuit means for reducing the amount of power that is applied to the electronic device in response to the third means.
 33. The circuit of claim 32 further including fifth circuit means for producing a signal indicative of an occurrence of the overcurrent event.
 34. The circuit of claim 32 further including a first connection terminal and a second power connection terminal, the power connection terminals suitable for connection to the power source, the third circuit means operable to detect an overcurrent event by monitoring electrical activity on only one of the first and second connection terminals.
 35. The circuit of claim 32 further including fifth circuit means for detecting electrical noise in the power, the second circuit means further being responsive to the fifth circuit means by varying the amount of power that is applied to the electronic device.
 36. The circuit of claim 32 wherein the fourth circuit means is effective for decoupling the power supply from the electronic device.
 37. A circuit for coupling a power source to a device comprising: first circuit means for detecting a connection event wherein a connection is made between the first circuit and the power source; second circuit means, responsive to the first circuit means, for coupling power from the power source to the device, the second circuit means operable to vary the amount of power that is applied to the device; third circuit means for detecting a change in an electrical parameter of the second circuit means indicative of a disconnection between the circuit and the power source; fourth circuit means for decoupling the power source from the device in response to the third means.
 38. The method of claim 37 further including fifth circuit means for producing a signal indicative of an occurrence of the disconnection between the circuit and the power source.
 39. The circuit of claim 37 further including fifth circuit means for detecting electrical noise in the power source, the second circuit means further being responsive to the fifth circuit means by varying the amount of power that is applied to the device.
 40. A circuit for coupling a power source to a device comprising: first circuit means for detecting a connection event wherein a connection is made between the circuit and the power source; second circuit means, responsive to the first circuit means, for providing a varying amount of power from the power source to the device; third circuit means for detecting when the device draws current from the power source exceeding a predetermined level of current; fourth circuit means for decoupling the power source from the device in response to the third means; fifth circuit means for detecting a change in an electrical parameter of the second circuit means indicative of a disconnection between the circuit and the power source; and sixth circuit means for decoupling the power source from the device in response to the fifth means.
 41. The circuit of claim 40 further including seventh circuit means for detecting electrical noise in the power, the second circuit means further being responsive to the seventh circuit means by varying the amount of power that is applied to the device. 